Perpendicular Recording Media Having an Exchange-Spring Structure

ABSTRACT

A recording medium providing improved writeability in perpendicular recording applications includes a magnetic recording layer having an axis of magnetic anisotropy substantially perpendicular to the surface thereof, an exchange-spring layer ferromagnetically exchange coupled to the magnetic recording layer and having a coercivity less than the magnetic recording layer coercivity, and a coupling layer between the magnetic recording layer and the exchange-spring layer. The coupling layer regulates the ferromagnetic exchange coupling between the magnetic recording layer and the exchange-spring layer.

RELATED APPLICATIONS

This application is a continuation application of and claims priorityto, co-pending application Ser. No. 11/231,516 filed on Sep. 21, 2005and entitled “PERPENDICULAR RECORDING MEDIA HAVING AN EXCHANGE-SPRINGSTRUCTURE” which claims the benefit of application Ser. No. 11/051,536filed on Feb. 4, 2005 issued as U.S. Pat. No. 7,425,377 which isincorporated herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to perpendicular magnetic recording media andmore particularly to apparatus and methods for improving thewriteability of perpendicular magnetic recording media.

2. Description of the Related Art

One of the primary challenges to increasing areal densities of magneticrecording media is overcoming the constraints imposed by thesuperparamagnetic effect. The superparamagnetic effect becomessignificant when microscopic magnetic grains on the recording mediabecome so small that they lose their ability to maintain their magneticorientations. This condition may result in “flipped bits,” a conditionwhere the magnetization of the bits suddenly and spontaneously reversesfrom north to south. Such a condition corrupts the data stored on themedia, rendering the data as well as the storage device it is stored onunreliable and unusable.

In conventional longitudinal recording media, data bits are alignedhorizontally, parallel to the surface of the disk. In perpendicularrecording media, the data bits are aligned vertically, perpendicular tothe disk. For example, referring to FIG. 1, a typical perpendicularrecording device 100 may include a recording head 102 and a magneticrecording medium 104. The recording head 102 may include a write element106, for writing magnetic signals to the recording medium 104, and aread element 108, to detect magnetic signals stored on the recordingmedium 104.

The magnetic recording medium 104 may include a magnetic recording layer110, to store data, and a soft underlayer 112 to provide a return pathfor magnetic write fields generated by the write element 106. Themagnetic recording layer 110 may comprise various magnetic grains eachhaving a magnetic easy axis substantially perpendicular to the mediasurface, thereby allowing the grains to be vertically magnetized. Whenwriting, the write element 106 generates a magnetic write field 116 thattravels vertically through the magnetic recording layer 110 and returnsto the write element 106 through the soft underlayer 112. In thismanner, the write element 106 magnetizes vertical regions 114, or bits114, in the magnetic recording layer 110. Because of the easy axisorientation, each of these bits 114 has a magnetization 118 that pointsin a direction substantially perpendicular to the media surface.

Because of the ability to utilize a soft underlayer in the perpendiculargeometry, write fields generated by the perpendicular write element 106may be substantially larger than conventional longitudinal recordingwrite fields. This allows use of media 104 having a higher coercivity(Hc) and anisotropy energy (Ku), which is more thermally stable.Furthermore, unlike longitudinal recording, where the magnetic fieldsbetween two adjacent bits have a destabilizing effect, the magneticfields of magnetization 118 of bits in perpendicular recording media 104stabilize each other, enhancing the overall stability of perpendicularmagnetic recording media even further. This allows for closer bitpacking.

Referring to FIG. 2, as mentioned, one benefit of perpendicularrecording is that the magnetic recording medium 104 is placed within thegap between the write element 106 and the soft underlayer 112, therebyallowing significantly higher write fields. When the write element 106is writing the magnetic recording layer 110, the soft underlayer 112reacts to the applied field of write element 106 in such a way that amirror image 200 of the write element 106, or a secondary write pole200, is generated in the soft underlayer 112. The write element 106 andthe secondary write pole 200 together produce an apparent recording head106, 200. In certain embodiments, the magnetic recording medium 104 mayinclude an non-magnetic overcoat 202, above the magnetic recording layer110, and an exchange break layer 204 to magnetically decouple themagnetic recording layer 110 from the soft underlayer 112.

One of the problem for conventional perpendicular media is that themagnetization 206, or magnetic easy axis 206, of the magnetic recordinglayer 110 is oriented nearly parallel to the magnetic field 116. Thisgeometry has the disadvantage that relatively high reversal fields arenecessary to reverse the magnetization 206 of the grains 208 of themagnetic recording layer 100 because little or no torque is exerted ontothe grain magnetization 206 by the magnetic write field 116.Furthermore, such a nearly parallel alignment of field 116 andmagnetization 206 has the additional disadvantage that the magnetizationreversal time of the media grains 208 is increased. For these reasons,there have been proposals to produce magnetic media comprising magneticgrains having a magnetic easy axis that is tilted, or non-parallel, withrespect to the surface normal. However, at the present time, apparatusand methods for producing high-quality recording media with a uniformlytilted easy axis do not exist.

Accordingly, what are needed are apparatus and methods for improving thewriteability of perpendicular magnetic recording media. Further neededare apparatus and methods for producing perpendicular magnetic recordingmedia that behaves like media with a tilted easy axis, while still beingfully compatible with currently used processes and structures forproducing perpendicular recording media. Such apparatus and methods aredisclosed herein.

SUMMARY OF THE INVENTION

The present invention has been developed in response to the presentstate of the art, and in particular, in response to the problems andneeds in the art that have not yet been fully solved by currentlyavailable apparatus and methods. Accordingly, the present invention hasbeen developed to provide apparatus and methods for improving thewriteability of perpendicular magnetic recording media that overcomemany or all of the above-discussed shortcomings in the art.

In one embodiment in accordance with the invention, a recording mediumproviding improved writeability in perpendicular recording applicationsincludes a magnetic recording layer having an axis of magneticanisotropy substantially perpendicular to the surface thereof, anexchange-spring layer ferromagnetically exchange coupled to the magneticrecording layer and having a coercivity less than the magnetic recordinglayer coercivity, and a coupling layer between the magnetic recordinglayer and the exchange-spring layer. The coupling layer regulates theferromagnetic exchange coupling between the magnetic recording layer andthe exchange-spring layer. Preferably, the coupling layer has athickness less than the exchange-spring layer thickness. The magneticrecording layer and the exchange-spring layer comprise a granular cobaltalloy suitable to achieve an appropriate and sufficiently low level ofinter-granular exchange coupling within each respective layer.

In certain embodiments, the exchange-spring layer, the magneticrecording layer, or both, may comprise a material such as CoPt, CoPtCr,and may optionally include an oxide such as a Si, Ti, and Ta oxide. Inselected embodiments, the coercivities of the magnetic recording layerand the exchange-spring layer are adjusted by among other processparameters modifying the amount of platinum therein. The coupling layermay comprise a material such as CoRu, CoCr, CoRuCr, and may optionallycomprise an oxide such as a Si, Ti, and Ta oxide.

In certain embodiments, the coupling layer has a thickness of less thantwo nanometers. More particularly, the coupling layer may have athickness of between 0.2 nanometers and 1 nanometer. Likewise, incertain embodiments, the exchange-spring layer has a thickness of lessthan ten nanometers and, more particularly, may have a thickness ofbetween two nanometers and six nanometers. In selected embodiments, theexchange-spring layer is thicker than the coupling layer. Furthermore,in certain embodiments, the inter-granular exchange coupling of theexchange-spring layer is greater than the inter-granular exchangecoupling of the magnetic recording layer.

In another embodiment in accordance with the invention, a recordingdevice providing improved writeability in perpendicular recordingapplications includes a recording head and a recording medium configuredfor perpendicular recording. The recording medium comprises a magneticrecording layer having an axis of magnetic anisotropy substantiallyperpendicular to the surface thereof, an exchange-spring layer betweenthe magnetic recording layer and the recording head, the exchange-springlayer ferromagnetically exchange coupled to the magnetic recording layerand having a coercivity less than the magnetic recording layercoercivity, and a coupling layer between the magnetic recording layerand the exchange-spring layer. The coupling layer regulates theferromagnetic exchange coupling between the magnetic recording layer andthe exchange-spring layer. The magnetic recording layer and theexchange-spring layer preferably comprise a granular cobalt alloy.

In another embodiment in accordance with the invention, a method forimproving the writeability of perpendicular recording media includesforming a magnetic recording layer having an axis of anisotropysubstantially perpendicular to the surface thereof, forming anexchange-spring layer comprising substantially magnetically separatedgrains, the exchange-spring layer ferromagnetically exchange coupled tothe magnetic recording layer and having a coercivity less than themagnetic recording layer coercivity, and disposing a coupling layerbetween the magnetic recording layer and the exchange-spring layer, thecoupling layer regulating the ferromagnetic exchange coupling betweenthe magnetic recording layer and the exchange-spring layer. Theexchange-spring layer preferably comprises a granular cobalt alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating one embodiment of aconventional perpendicular recording device;

FIG. 2 is a cross-sectional view of one embodiment of conventionalperpendicular recording media;

FIG. 3 is a cross-sectional view of one embodiment of perpendicularrecording media using an exchange-spring structure in accordance withthe invention;

FIG. 4 is a schematic diagram illustrating the magnetization reversal ofperpendicular recording media using an exchange-spring structure inaccordance with the invention;

FIG. 5A is a graph illustrating one embodiment of a magnetic hysteresisloop for the magnetic recording layer by itself;

FIG. 5B is a graph illustrating one embodiment of a magnetic hysteresisloop for the exchange-spring layer by itself;

FIG. 5C is a graph illustrating one embodiment of a magnetic hysteresisloop for an exchange-spring structure in accordance with the invention;

FIG. 6A is a graph illustrating the low frequency signal amplitudeversus the write current for an exchange-spring structure having anexchange-spring layer thickness of three nanometers and various couplinglayer thicknesses, the graph compares exchange-spring structures to areference media without an exchange spring structure;

FIG. 6B is a graph illustrating the normalized low frequency signalamplitude versus the write current for an exchange-spring structurehaving an exchange-spring layer thickness of three nanometers andvarious coupling layer thicknesses, the graph compares exchange-springstructures to a reference media without an exchange spring structure;

FIG. 7A is a graph illustrating the signal-to-noise ratio versus therecording density for an exchange-spring structure having anexchange-spring layer thickness of three nanometers and various couplinglayer thicknesses, the graph compares exchange-spring structures to areference media without an exchange spring structure;

FIG. 7B is a graph illustrating the signal-to-noise ratio versus thecoupling layer thickness for an exchange-spring structure having anexchange-spring layer thickness of three nanometers and for a target bitlength (1T) and twice the target bit length (2T), the graph comparesexchange-spring structures to a reference media without an exchangespring structure; and

FIG. 8 is a graph illustrating the bit error rate versus the couplinglayer thickness for an exchange-spring structure having anexchange-spring layer thickness of three nanometers, the graph comparesexchange-spring structures to a reference media without an exchangespring structure.

DETAILED DESCRIPTION OF THE INVENTION

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the embodimentis included in at least one embodiment of the present invention. Thus,appearances of the phrases “in one embodiment,” “in an embodiment,” andsimilar language throughout this specification may, but do notnecessarily, all refer to the same embodiment.

Furthermore, the described features, structures, or characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. In the following description, numerous specific details aredisclosed to provide a thorough understanding of embodiments of theinvention. One skilled in the relevant art will recognize, however, thatthe invention may be practiced without one or more of the specificdetails, or with other methods, components, materials, and so forth. Inother instances, well-known structures, materials, or operations are notshown or described in detail to avoid obscuring aspects of theinvention.

For the purposes of this description, the phrase “axis of magneticanisotropy” is used to mean the magnetic easy axis of a magneticmaterial.

Referring to FIG. 3, a perpendicular magnetic recording medium 300incorporating an exchange-spring structure 301 in accordance with theinvention may comprise a magnetic recording layer 302 ferromagneticallycoupled to an exchange-spring layer 304. The magnetic recording layer302 and the exchange-spring layer 304 are preferably layers of agranular cobalt alloy with a hexagonal close packed (hcp) crystallinestructure that exhibit perpendicular magnetic anisotropy, such as a CoPtor CoPtCr alloys, with or without an oxide, such as oxides of Si, Ti andTa. However, while the magnetic recording layer 302 may be relativelyhard magnetically (e.g., Hk>10 kOe), the exchange spring layer 304 maybe considerably softer (e.g., Hk<6 kOe). In certain embodiments, themagnetic recording layer 302 and the exchange-spring layer 304 are of asame or similar material and the coercivity of each is adjusted alongwith other processing parameters by modifying the amount of platinumcontained therein. A higher proportion, or concentration, of platinumper volume of the magnetic recording layer 302 relative to the exchangespring layer 304 will increase the magnetic hardness of the recordinglayer 302 relative to the exchange spring layer 304.

The materials specified above may be suitable to achieve an appropriate(i.e., low) level of inter-granular exchange coupling in the magneticrecording layer 302 and the exchange spring layer 304, respectively.Although, the inter-granular exchange coupling of the exchange springlayer 304 may exceed that of the magnetic recording layer 302, it ispreferable that the inter-granular exchange coupling of the exchangespring layer 304 be sufficiently low to minimize or reduce negativeeffects, such as lower signal-to-noise ratio or the like, that a higherinter-granular exchange coupling might have on the magnetic recordinglayer 302. In certain embodiments, the exchange-spring layer has athickness of less than ten nanometers, and more preferably between abouttwo nanometers and six nanometers.

A coupling layer 306 is disposed between the magnetic recording layer302 and the exchange-spring layer 304 to regulate or mediate theexchange coupling between the two layers 302, 304. This aids themagnetization reversal process of the magnetic recording layer 302 byexerting an additional bias field and torque on the grains of themagnetic recording layer 302 upon applying a reverse magnetic field. Thecoupling layer 306 is preferably a weakly magnetic or non-magneticgranular alloy layer with an hcp crystalline structure, such as a CoRu,CoCr or CoRuCr alloy, with or without an oxide, such as oxides of Si,Ti, and Ta, which is suitable to mediate a ferromagnetic coupling ofappropriate strength between the magnetic recording layer 302 and theexchange-spring layer 304. Depending on the choice of material, and moreparticularly on the concentration of cobalt in the coupling layer 306,the coupling layer 306 may have a thickness of less than two nanometers,and more preferably between about 0.2 nanometers and 1 nanometer.Although in certain embodiments, the thickness of the coupling layer 306may exceed 1 nanometer. Because cobalt is highly magnetic, a higherconcentration of cobalt in the coupling layer 306 may be offset bythickening the coupling layer 306 in order to achieve an optimalinter-layer exchange coupling between the magnetic recording layer 302and the exchange-spring layer 304.

As will be discussed in more detail hereinafter, the inter-layerexchange coupling between the magnetic recording layer 302 and theexchange-spring layer 304 may be optimized, in part, by adjusting thematerials and thickness of the coupling layer 306. Preferably, theinter-layer exchange coupling is not so weak that the exchange-springlayer 304 and the magnetic recording layer 302 behave as independententities. Likewise, the inter-layer exchange coupling is preferably notso strong that the magnetic behavior of the exchange-spring layer 304and the magnetic recording layer 302 are rigidly bound together. Theinter-layer exchange coupling should be adjusted such that themagnetization of the exchange-spring layer 304 reverses before that ofthe magnetic recording layer 302, while exerting enough torque onto thegrains of the magnetic recording layer 302 to aid in the magneticreversal of the magnetic recording layer 302.

Furthermore, as mentioned, in preferred embodiments, the exchange-springlayer 304 is magnetically softer (lower coercivity) than the magneticrecording layer 302. Also, the exchange-spring layer 304 may becharacterized by an inter-granular exchange coupling that is greaterthan the inter-granular exchange coupling of the magnetic recordinglayer 302. By adjusting the thickness and materials of the couplinglayer 306 to optimize the inter-layer exchange coupling between theexchange-spring layer 304 and the magnetic recording layer 302, negativeeffects caused by the exchange-spring layer's 304 higher inter-granularexchange coupling, such as lower signal-to-noise ratios or the like, maybe at least partially isolated from the magnetic recording layer 302.

In certain embodiments, an overcoat 308 may be physically and preferablynot magnetically coupled to the exchange-spring layer 304. Similarly,the magnetic recording layer 302 may be physically coupled to a softunderlayer 312 by way of an exchange-break layer 310. The softunderlayer 312 may be a multi-layer structure that provides a mirrorimage 314 (i.e., a secondary write pole 314) of a real write head 316,thereby allowing large write fields to pass through the media 300. Theexchange-break layer 310 may be used to magnetically decouple themagnetic recording layer 302 from the soft underlayer 312.

Referring to FIG. 4, absent a magnetic field and prior to reversal, themagnetization 400 a, 402 a of both the exchange-spring layer 304 and themagnetic recording layer 302 may point in either a north or southdirection. Upon applying a reverse magnetic field 404 a, themagnetization 400 b of the softer exchange-spring layer 304 may begin toreverse, thereby exerting a torque onto the magnetically harder magneticrecording layer 302. As the magnetic field 404 b increases, themagnetization 402 c of the magnetic recording layer 302 begins toreverse and follow the magnetization 400 c of the exchange-spring layer304. Finally, as the magnetic field 404 c increases further, themagnetization 400 d, 402 d of both the exchange-spring layer 304 and themagnetic recording layer 302 reverses entirely. Advantageously, theexchange-spring media 300 exhibits a magnetization reversal behaviorwhich is similar to a magnetic recording layer having a tilted magneticeasy axis, while still being fully compatible with conventionalperpendicular media deposition and fabrication processes and structures.

Referring to FIGS. 5A through 5C, several hysteresis loops generatedwith a Kerr magnetometer are illustrated for the magnetic recordinglayer 302 by itself (FIG. 5A), the exchange-spring layer 304 by itself(FIG. 5B), and an exchange spring structure 301 comprising both themagnetic recording layer 302 and the exchange-spring layer 304 coupledtogether with a coupling layer 306 (FIG. 5C) in accordance with thepresent invention. In this example, the magnetic recording layer 302 iscobalt platinum chromium tantalum oxide (CoPtCrTaOx), theexchange-spring layer 304 is cobalt platinum chromium silicon oxide(CoPtCrSiOx), and the coupling layer 306 is cobalt ruthenium (CoRu).

As illustrated by FIGS. 5A and 5B, the narrower hysteresis loop of FIG.5B compared to that of FIG. 5A shows that the coercivity of theCoPtCrSiOx exchange-spring layer 304 by itself is less than that of theCoPtCrTaOx magnetic recording layer 302 by itself. This is true even fora CoPtCrSiOx exchange-spring layer 304 that is sixteen nanometers thick.When the CoPtCrSiOx exchange-spring layer 304 is thinned (as in theexchange-spring structure 301 of FIG. 3), the coercivity of theexchange-spring layer 304 is significantly less as shown by the steeperslope 500 of the hysteresis loop of FIG. 5C. The subsequentmagnetization of the magnetically harder magnetic recording layer 302 isshown by the slower approach to saturation 502, as shown by the reducedslope 504 of the hysteresis loop.

As illustrated by FIG. 5C, when the CoPtCrTaOx magnetic recording layer302 and CoPtCrSiOx exchange-spring layer 304 are combined into anexchange-spring structure 301 like that illustrated in FIG. 3 with aCoRu layer as the coupling layer 306 the hysteresis loop of FIG. 5Ccloses for a magnetic field (H) of approximately 9 kOe, whereas thehysteresis loop of FIG. 5A closes for a magnetic field (H) ofapproximately 12 kOe, showing that all or most of the grains of theexchange-spring structure 301 of FIG. 5C may be switched with a magneticfield reduced by approximately twenty-five percent.

Referring to FIGS. 6A and 6B, the low-frequency signal amplitude (LFTAA)versus the write current (I(mA)) is illustrated for a thickness of 3 nmfor the exchange-spring layer 304 and various thicknesses of thecoupling layer 306. In this example, the exchange-spring layer 304 isCoPtCrSiOx and the coupling layer 306 is CoRu. The reference layer isCoPtCrTaOx magnetic recording media without the exchange-spring layer304 or the coupling layer 306.

As illustrated in FIG. 6A, for an exchange-spring structure 301 with anexchange-spring layer 304 having a thickness of three nanometers and acoupling layer 306 having a thickness of four or six angstroms, thesignal amplitude saturates at lower write currents compared to thereference layer demonstrating that these structures are easier to write.These exchange-spring structures 301 also have higher signal amplitudesthan the reference layer indicating that these structures add to thesignal. If the CoRu layer thickness is increased to nine angstroms,however, the inter-layer exchange coupling between the exchange-springlayer 304 and the magnetic recording layer 302 is reduced and thewriting improvements substantially disappear. FIG. 6A also illustratesthat the signal amplitude and saturation for a nine angstrom couplinglayer 306 either tracks, or is only marginally higher than the referencelayer. In FIG. 6B, which shows the normalized signal of the data shownin FIG. 6A, the pure writability improvement becomes more evidentbecause the writability improvement has been separated from thesimultaneously occurring signal increase as the coupling layer 306thickness is reduced.

Referring to FIGS. 7A and 7B, the signal-to-noise ratio (SNR) isillustrated versus the recording density (FIG. 7A) and the couplinglayer thickness (FIG. 7B). As illustrated by FIG. 7A, an exchange-springstructure 301 having a CoPtCrSiOx exchange-spring layer 304 that isthree nanometers thick and a CoRu coupling layer 306 that is three orsix angstroms thick has a better or higher signal-to-noise ratio thanthe CoPtCrTaOx recording media reference layer alone. An exchange-springstructure 301 having a CoPtCrSiOx exchange-spring layer 304 that isthree nanometers thick and a CoRu coupling layer 306 that is nineangstroms thick, on the other hand, has a worse signal-to-noise ratiothan the reference layer. Of course those of skill in the art willrecognize that the specific thickness of the CoRu coupling layer 306that provides satisfactory signal-to-noise ratios may be different whenthe coupling layer 306 comprises different materials or compositionsalong with, or in place of, Co and Ru.

FIG. 7B illustrates the signal-to-noise ratio for an exchange springstructure 301 having different thicknesses for the coupling layer 306.The signal-to-noise ratio is illustrated for both a target bit length(1T) and double the target bit length (2T). As can be seen from FIG. 7B,the signal-to-noise ratio for 1T data has a lower signal-to-noise ratiothan the 2T data since the density is doubled. As further illustrated byFIG. 7B, the signal-to-noise ratio improves for an exchange-springstructure 301 with a three nanometer CoPtCrSiOx exchange-spring layer304 in an intermediate thickness range of the coupling layer 306 forboth a 1T (corresponding to a target bit length indicated by the solidsquare shapes 700) and a 2T (corresponding to twice the target bitlength indicated by the solid circle shapes 702) measurement, comparedto a CoPtCrTaOx reference layer by itself (indicated by the open shapes704). As is also illustrated by FIG. 7B, once the coupling layer 306reaches approximately eight angstroms, the signal-to-noise ratio fallsbelow the signal-to-noise ratio of the reference layer. Thus, FIGS. 7Aand 7B indicate that a coupling layer 306 in the range of four to sevenangstrom provides a better signal-to-noise ratio than the referencelayer alone, at least for a Co₂₀Ru₈₀ coupling layer 306. For couplinglayers 306 comprising other materials or compositions, the optimalthickness may change.

Referring to FIG. 8, the bit error rate versus the CoRu coupling layer306 is illustrated for an exchange-spring structure 301 having aCoPtCrSiOx exchange-spring layer 304 that is three nanometers thick. Asillustrated, the improved signal-to-noise ratio shown in FIGS. 7A and 7Bis reflected by an improved error rate, where the error rate of theexchange-spring structure is improved significantly with respect to aCoPtCrTaOx reference layer (indicated by empty square shape 802) in theCoRu coupling layer 306 thickness range of four to seven angstrom.

The higher signal-to-noise ratios and bit error rates for the exchangespring structure 301 as illustrated by FIGS. 7A, 7B, and 8 illustratethat the unique materials and thicknesses used for the exchange springlayer 304 and the coupling layer 306, as recited in the claims, doimprove the signal-to-noise ratio and bit error rate of the referencelayer, or the magnetic recording layer 302, by itself. This isadvantageous in comparison to conventional exchange spring structures,where the magnetically softer exchange spring layer often worsens thesignal-to-noise ratio and bit error rate of the underlying magneticrecording layer.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A recording medium providing improved writeability in perpendicularrecording applications, the recording medium comprising: a magneticrecording layer having a first coercivity and an axis of magneticanisotropy substantially perpendicular to the surface thereof; and anexchange-spring layer having a second coercivity less than the firstcoercivity, the exchange-spring layer ferromagnetically exchange coupledto the magnetic recording layer, wherein a magnetization of theexchange-spring layer begins to reverse before a magnetization of themagnetic layer completely reverses such that the magnetization of theexchange-spring layer exerts a torque on the magnetic recording layer.2. The recording medium of claim 1, wherein the magnetic recording layerand the exchange-spring layer comprise a granular cobalt alloy andwherein either granular cobalt alloy comprises an alloy selected fromthe group consisting of CoPt and CoPtCr.
 3. The recording medium ofclaim 2, wherein either granular cobalt alloy further comprises an oxideselected from the group consisting of an Si, Ti, and Ta oxide.
 4. Therecording medium of 2, wherein the magnetic recording layer comprises ahigher concentration of platinum than the exchange-spring layer suchthat the first coercivity is greater than the second coercivity.
 5. Therecording medium of claim 1, further comprising a coupling layer betweenthe magnetic recording layer and the exchange-spring layer, the couplinglayer comprising a material selected from the group consisting of CoRu,CoCr, CoRuCr, and alloys thereof.
 6. The recording medium of claim 5,wherein the coupling layer further comprises an oxide selected from thegroup consisting of an Si, Ti, and Ta oxide.
 7. The recording medium ofclaim 1, further comprising a coupling layer between the magneticrecording layer and the exchange-spring layer, wherein the couplinglayer has a thickness of less than about two nanometers.
 8. Therecording medium of claim 7, wherein the coupling layer has a thicknessof between about 0.2 nanometers and about 1 nanometer.
 9. The recordingmedium of claim 1, wherein the exchange-spring layer has a thickness ofless than about ten nanometers.
 10. The recording media of claim 9,wherein the exchange-spring layer has a thickness of between about twonanometers and about six nanometers.
 11. The recording medium of claim1, wherein the magnetic recording layer and the exchange-spring layerare characterized by an inter-granular exchange coupling, theinter-granular exchange coupling of the exchange-spring layer beinggreater than the inter-granular exchange coupling of the magneticrecording layer.
 12. The recording medium of claim 1, further comprisinga soft underlayer physically coupled to the magnetic recording layer byway of an exchange break layer, the exchange break layer magneticallydecoupling the soft underlayer from the magnetic recording layer.
 13. Arecording device providing improved writeability in perpendicularrecording applications, the recording device comprising: a recordinghead for reading magnetic signals from, and writing magnetic signals to,a recording medium; and a recording medium configured for perpendicularrecording, the recording medium comprising: a magnetic recording layerhaving a first coercivity and an axis of magnetic anisotropysubstantially perpendicular to the surface thereof; an exchange-springlayer interposed between the magnetic recording layer and the recordinghead, the exchange-spring layer having a second coercivity less than thefirst coercivity, wherein a magnetization of the exchange-spring layerbegins to reverse before a magnetization of the magnetic layercompletely reverses such that the magnetization of the exchange-springlayer exerts a torque on the magnetic recording layer.
 14. The recordingdevice of claim 13, wherein the magnetic recording layer and theexchange-spring layer comprising a granular cobalt alloy and whereineither granular cobalt alloy comprises an alloy selected from the groupconsisting of CoPt and CoPtCr.
 15. The recording device of claim 14,wherein either granular cobalt alloy further comprises an oxide selectedfrom the group consisting of an Si, Ti, and Ta oxide.
 16. The recordingdevice of 14, wherein the magnetic recording layer comprises a higherconcentration of platinum than the exchange-spring layer such that thefirst coercivity is greater than the second coercivity.
 17. Therecording device of claim 13, further comprising a coupling layerbetween the magnetic recording layer and the exchange-spring layer, thecoupling layer regulating the ferromagnetic exchange coupling betweenthe magnetic recording layer and the exchange-spring layer, wherein thecoupling layer comprises a material selected from the group consistingof CoRu, CoCr, CoRuCr, and alloys thereof.
 18. The recording device ofclaim 17, wherein the coupling layer further comprises an oxide selectedfrom the group consisting of an Si, Ti, and Ta oxide.
 19. The recordingdevice of claim 13, further comprising a coupling layer between themagnetic recording layer and the exchange-spring layer, wherein thecoupling layer has a thickness less than the exchange-spring layer. 20.The recording device of claim 19, wherein the coupling layer has athickness of between about 0.2 nanometers and about 1 nanometer.
 21. Therecording device of claim 13, wherein the exchange-spring layer has athickness of less than about ten nanometers.
 22. The recording device ofclaim 21, wherein the exchange-spring layer has a thickness of betweenabout two nanometers and about six nanometers.
 23. The recording deviceof claim 22, wherein the magnetic recording layer and theexchange-spring layer are characterized by an inter-granular exchangecoupling, the inter-granular exchange coupling of the exchange-springlayer being greater than the inter-granular exchange coupling of themagnetic recording layer.
 24. A method for improving the writeability ofmagnetic perpendicular recording media, the method comprising: forming amagnetic recording layer having a first coercivity and an axis ofmagnetic anisotropy substantially perpendicular to the surface thereof;and forming an exchange-spring layer having a second coercivity lessthan the first coercivity, the exchange-spring layer ferromagneticallyexchange coupled to the magnetic recording layer, wherein amagnetization of the exchange-spring layer begins to reverse before amagnetization of the magnetic layer completely reverses such that themagnetization of the exchange-spring layer exerts a torque on themagnetic recording layer.
 25. The method of claim 24, further comprisingdisposing a coupling layer between the magnetic recording layer and theexchange-spring layer, the coupling layer regulating the ferromagneticexchange coupling between the magnetic recording layer and theexchange-spring layer, wherein the coupling layer comprises a materialselected from the group consisting of CoRu, CoCr, and CoRuCr.
 26. Themethod of claim 24, wherein the coupling layer has a thickness of lessthan about two nanometers.
 27. The method of claim 24, wherein theexchange-spring layer has a thickness of less than about ten nanometers.28. The method of claim 24, wherein the magnetic recording layer and theexchange-spring layer are characterized by an inter-granular exchangecoupling, the inter-granular exchange coupling of the exchange-springlayer being greater than the inter-granular exchange coupling of themagnetic recording layer.